The long-term goal of this research program is to comprehensively understand the function and regulation of the proteasome in intracellular protein degradation. Proteasome-dependent protein degradation, principally via the ubiquitin pathway, regulates critical processes including transcription, the cell cycle, signal transduction, antigen processing, quality control, and growth and atrophy of tissues. The proteasome [unreadable] is a modular system consisting of multiple forms of catalytic 20S proteasomes and multiple regulatory proteins. Interchangeable binding of proteasomes and regulatory proteins produces different proteasome forms with unique biochemical and physiological properties, and probably explains how the proteasome can participate in its varied cellular functions. Despite their likely importance, the biochemical and cellular mechanisms that determine relative interactions among proteasome components are poorly defined. This project will examine the role of subcellular distribution as a mechanism for proteasome regulation, using the nucleus as an example. Specific Aim 1 will define and compare qualitative and quantitative distribution of proteasome system components among whole cells, the nucleus, and subnuclear PML bodies under various physiological and pathological states. Specific Aim 2 will determine the role of VCP, a putative proteasome binding ATPase, in localization of proteasome system components and substrates to nuclear PML bodies and cytoplasmic aggresomes. Specific Aim 3 will examine mechanisms by which the proteasome regulator, PA28, is localized to nuclear PML bodies; the role of PA28 modification by the ubiquitin-like protein, SUMO, in this process will be determined. Specific Aim 4 will determine the mechanism by which PMLp, the principal component of PML bodies, is degraded by the proteasome, and will examine both the subcellular location and the relative roles of PMLp modification by SUMO and ubiquitin in this process. These experiments will test the hypothesis that proteasome-dependent PMLp degradation regulates content and function of PMLp at PML bodies. Completion of these specific aims will provide critical new information about the features, mechanisms, and functions of localized forms of the proteasome system. [unreadable] [unreadable]